1. Field of the Invention
The invention relates to a shoe structure, which is at least part of a shoe and consists of: an upper, comprising at least one outer layer and a lining, which lines the inside of the outer layer and includes a waterproof and water-vapour permeable functional layer; a first insole which closes the underside of the inner area of the shoe structure; a second insole and an outsole which is bonded to the second insole, whereby the lower end area is turned back to the inside and positioned against the second insole and bonded to it in a watertight manner, and whereby the second insole has an outer edge around its periphery, the outer edge having a contour corresponding to the contour of the lower end area of the outer layer and joined to the lower end area of the outer layer.
2. Description of the Related Art
A cement-lasted shoe structure of this kind is already known from DE-OS 40 07 962. In the shoe structure described in that publication, it is a prerequisite that the second insole itself must be waterproofed, in that it also includes a waterproof and water-vapour permeable layer on its side which faces the lining, and that the lining has the waterproof, water-vapour permeable functional layer on its side which faces the outer layer. It is not possible in practice to use the known construction in other types of shoe, for example in a Strobel shoe structure (shoe structure in which the second insole is sewn to the outer layer with a sewing machine manufactured by Strobel) or a flex construction shoe structure (the outer layer is turned back to the outside in the lower area and sewn to an insole in the turned-back area).
In the embodiment described in DE-OS 40 07 962, it is not possible when bonding the second insole to the functional layer of the lining to guarantee that the adhesive will form a waterproof connection over the entire surface between the lining and second insole. For this reason, it is readily possible for water to penetrate between the lining and the second insole. Also, the functional layer is heavily stressed when the shoe is worn, which often causes cracks to form in the functional layer or causes the adhesive in the connecting area between the functional layer and second insole to break open, allowing water to penetrate unhindered to the inner area of the shoe.
In an attempt to protect the waterproof, water-vapour permeable functional layer from heavy mechanical stress, it has become common practice to reinforce this functional layer from the outside with a textile material. When functional layers of this kind are used, it is almost impossible to form a waterproof connection between the functional layer and the second insole, because it cannot be guaranteed that the adhesive will penetrate fully the textile reinforcing material which is now positioned between the functional layer and the second insole. Consequently, channels through which water is able to penetrate into the inner area of the shoe structure are already formed during production of the shoe structure. Even if the formation of larger channels can be avoided, microchannels form in the connection area between the lining and the second insole, which are saturated by water drawn in by capillary action.
For this reason, it has become increasingly common in the production of shoe structures with good breathing properties, which are nevertheless waterproof and which contain a waterproof, water-vapour permeable functional layer, to use an injection moulded outsole, since apparently fewer problems related to water tightness occur when the outsole material is injection moulded. Also, this shoe structure design can be manufactured more economically.